duete; see due, ty 2 ]. syn: duty, obligation refer to something a person feels bound to do. A duty often applies to what a person performs in fulfillment of the permanent dictates of conscience, piety, right, or law: one's duty to tell the truth; a parent's duty to raise children properly.
Mutations in the RB1 gene are responsible for most cases of retinoblastoma. RB1 is a tumor suppressor gene, which means that it normally regulates cell growth and keeps cells from dividing too rapidly or in an uncontrolled way.
Moreover, both the penetrance and expressivity of different diseases can be partially explained by the action of gene modifiers. Retinoblastoma is a cancer of the retina that primarily affects children and is caused by mutations in the Rb gene.